The International Olympic Committee’s handling of Russia’s systemic doping program has been plunged into disarray after sport’s top court overturned bans issued to 28 Russian athletes just days before the start of the Winter Games in Pyeongchang, South Korea.

The Court of Arbitration for Sport ruled Thursday that there was insufficient evidence that the athletes — including some medal winners — breached antidoping regulations at the 2014 Olympics in Sochi, Russia. The reversal means athletes deemed to have been part of an elaborate cheating scheme may yet compete in the Olympics. It is yet another blow to the credibility of the Olympic committee’s management of the doping affair.

The outcome raises yet more troubling questions about the lengthy and complicated process that defined the I.O.C’s treatment of the affair, and why experts in sporting jurisprudence, including I.O.C. President Thomas Bach, failed to predict Thursday’s outcome. Bach once led the court’s appeals division, and John Coates, a longtime senior I.O.C. member, is president of the court’s top board.

Skeptics say the judgment allows the I.O.C. the fig leaf of talking tough, while at the same time making decisions that it knowingly knew could be successfully challenged on appeal.

The scandal first surfaced on the eve of the Rio de Janeiro Summer Games in 2016. In December, after a lengthy and much-delayed investigation, a slew of athletes, coaches and officials were hit with sanctions, and the Russian Olympic Committee was barred from attending the Pyeongchang Games.

In a move criticized by many in the global antidoping community, the International Olympic Committee ruled that clean Russian individuals could compete in separate uniforms designating them as “Olympic athletes from Russia,” should they satisfy a review panel.

On Tuesday, 169 athletes from Russia were cleared to participate, making the contingent one of the largest at the Games, and just eight short of the 177 sent to compete in Vancouver, British Columbia, in 2010.

Russia’s deputy prime minister, Vitaly Mutko, a former sports minister now serving a life suspension from the Olympics, said the government would support further legal action to ensure the additional athletes cleared on Thursday could compete in Pyeongchang.

“If the I.O.C. does not accept them, then we will support them in cases which could be filed at C.A.S. and other legal instances,” Mutko said in televised comments, referring to the sports court.

The International Olympic Committee insisted that it retained the authority to decide who would be allowed to compete, regardless of the court’s decision.

“The result of the C.A.S. decision does not mean that athletes from the group of 28 will be invited to the Games,” it said. “Not being sanctioned does not automatically confer the privilege of an invitation.”

The sports court said it overturned the doping bans because “the evidence collected was found to be insufficient to establish that an antidoping rule violation was committed by the athletes concerned.”

The court found that 11 of the athletes had broken those rules, and upheld the ban on their competing in Pyeongchang, but it ruled that they could compete in future Olympics. Three appeals are pending, and one of the 43 athletes did not appeal the sanctions.

Russia celebrated the ruling. A state-backed sports broadcaster aired the nearly two-hour cross-country ski race won in 2014 by Alexander Legkov, one of the athletes whose appeal was upheld.

“We insisted from the very start that our athletes are not involved in any doping schemes, and, of course, we are now just happy that their honest name has been reinstated by court and all their awards have been returned to them,” said Alexander Zhukov, head of the Russian Olympic Committee.

“It proves our position that the vast majority of our athletes are clean,” Russian President Vladimir V. Putin said in televised comments from Rostov-on-Don. “We should also respect the side which we were in dispute with. That’s why there should not be any sense of euphoria from our side, we should be calm about it.”

The court of arbitration noted that it was not passing judgment on “whether there was an organized scheme allowing the manipulation of doping control samples in the Sochi laboratory,” but on the culpability of individual athletes.

In its statement, the I.O.C. lamented that the court of arbitration had not taken into account the “proven existence of the systematic manipulation of the antidoping system” by Russia.

The case against Russia was largely built on the bombshell testimony of the former head of its drug testing laboratory, Grigory Rodchenkov. Rodchenkov, now living in hiding in the United States, detailed how he had formulated cocktails of banned substances to athletes and swapped the tainted samples under the direction of government officials.

His testimony backed up laboratory data that allowed the Olympic committee to essentially concur with the conclusions about the existence of a systematic doping scheme made in a 2016 investigation by the Canadian lawyer Richard McLaren. Thomas Bach, the president of the International Olympic Committee, described it is an “unprecedented attack on the integrity of the Olympic Games and sport.”

Rodchenkov, the whistle-blower, had alleged that Russia had found a way to pry open supposedly tamper-proof drug-testing bottles and replace their contents without detection.

The arbitration panel rejected 11 appeals, including that of the two-time bobsled gold medalist Alexandr Zubkov. His retested samples had abnormal levels of salt, a substance, according to Rodchenkov, that was used to cover up doping violations in the swapped samples.

McLaren and Rodchenkov provided testimony to the Russian appeals hearings via video link. They were not interviewed by the Olympic committee panel that issued the original ban on the Russian athletes.

“Clean sport is dead,” Rodchenkov’s lawyer Jim Walden said. “The C.A.S. decision proves that certain countries can get away with anything and everything. Today’s decision will forever stand as the low point in sports integrity.”

“This panel’s unfortunate decision provides a very small measure of punishment for some athletes, but a complete ‘get out of jail free card’ for most. Thus, the C.A.S. decision only emboldens cheaters, makes it harder for clean athletes to win and provides yet another ill-gotten gain for the corrupt Russian doping system generally, and Putin specifically.”

Handling the fallout from the scandal has been a draining and damaging experience for the International Olympic Committee’s leadership. The run-up to the Rio Olympics was marred by indecision over whether to allow Russia to participate. The committee tossed the decision to individual federations, which led to some, including track and field, to issue a near-blanket ban on Russians. That ban remains in place.

Organizers of the Paralympics were more decisive, announcing a ban on the entire Russian contingent. Last week, they announced that ban remains in place, refusing to lift the restriction because of what they called an insufficient recovery from the doping scandal.

A version of this article appears in print on , on Page B8 of the New York edition with the headline: Reversal of Doping Bans Leaves 28 Russian Athletes in Limbo. Order Reprints | Today’s Paper | Subscribe